North Koreans gather near a Pyongyang rail station Tuesday to watch a TV announcer read a statement about the country's nuclear test. / North Korean TV via AFP/Getty Images

by Oren Dorell, USA TODAY

by Oren Dorell, USA TODAY

North Korea's latest nuclear test shows it is making steady progress toward a deliverable nuclear weapon, and the international community and China, its greatest trading partner and ally, have little influence to make it to stop, analysts say.

Based on seismic evidence, "we can say with certainty they're getting better at building their nuclear device," said Robert Avagyan of the Institute for Science and International Security, a think-tank focused on controlling the spread of nuclear weapons.

North Korea's economy is so isolated that even China, North Korea's No. 1 trading partner, political ally and patron, has little influence on North Korean decision-making, says James Acton, a proliferation expert at the Carnegie Endowment for International Peace.

"North Korea's economy is extremely isolated and focused on self-reliance," Acton said. Despite growing trade with China, there is "probably not much leverage there."

North Korea conducted its third nuclear test Tuesday as part of a program it has said will allow it build a bomb that can reach the USA. North Korea said the atomic test was merely its "first response" to what it called U.S. threats and it will continue with unspecified "second and third measures of greater intensity" if Washington maintains its hostility.

President Obama said the nuclear tests were a "highly provocative act" that endangers the USA and other Western nations." North Korea has "increasingly isolated and impoverished its people through its ill-advised pursuit of weapons of mass destruction," he said in a statement. In an emergency session, the United Nations Security Council unanimously said the test poses "a clear threat to international peace and security" and pledged further action.

Several nations, including Russia and China, have condemned the test. North Korea is subject to international sanctions that limit its trade with most of the world over its illegal nuclear program.

China summoned the North Korean ambassador to Beijing for a scolding and demanded that North Korea "swiftly return to the correct channel of dialogue and negotiation," according to the Chinese Ministry of Foreign Affairs.

Wu Qiang with the Department of Political Science at Tsinghua University in Beijing said China had publicly opposed the test this month and under its new leader, Xi Jinping, it may be less patient with the North.

"He may support South Korea and decrease petrol, rice and trade aid in the future to apply sanctions," Wu said.

China will also consider the reactions from ordinary Chinese toward the nuclear test, Wu said.

North Korea's third nuclear test produced a blast of about 10 kilotons, about twice as powerful as the test in 2009 and almost 10 times more powerful than the first test in 2006, Avagyan said. The U.S. bomb dropped on Hiroshima was a 12- to 20-kiloton blast, he said.

North Korea said the device it exploded was smaller than previous devices, but the question remains whether it would fit on a ballistic missile of the type that launched a satellite into orbit in December. North Korean officials said after that test that the their weapons program is aimed to deter the United States.

Rep. Mike Rogers, R-Mich., chairman of the House Intelligence Committee, said the Obama administration should lean on China to pressure its ally.

"The key to stemming North Korea's cycle of provocation is to seriously engage the Chinese in exercising leverage over their neighbor," Rogers said.

Professor Yu Chung Sik, a political expert in China's Shanghai International Studies University, says his country's influence on North Korea is waning. "China has less impact on North Korea than before," Yu said.

Acton said China has adopted a self-serving posture in which it benefits little from pressuring the North, given that China views its North Korean ally as a crucial buffer keeping the U.S. military from its border. Even if China had leverage, it probably would not use it for fear of bringing down the North Korean regime, Acton said.

Avagyan said China may respond to North Korea's defiance by signing on to international sanctions that prevent trade of so-called dual use items North Korea could use for its nuclear program. China could clamp down on a network of civilian-owned and North Korean front companies that funnel supplies for centrifuges, reactors, testing and delivery devices through China, he said.

Other analysts said the United States has tools for putting a tighter squeeze on North Korea's elite and military establishment and should use them.

"Go after the banks used by North Korea for illicit and provocative activity," said Bruce Bechtol, a former senior intelligence analyst at the Pentagon who's a professor at Angelo State University in San Angelo, Texas.

The tactic was effective in 2005, when the George W. Bush administration sanctioned Banco Delta Asia in Macao, which North Korea used to fund its weapons program. The bank blocked North Korean access to its funds, and other Asian banks blocked North Korea voluntarily, Bechtol said.

"North Korean officials ended up taking suitcases full of money across Asia, to Mongolia, to take care of their money," he said.

Bush suspended the program after North Korea agreed to dismantle its nuclear program in "six-party" talks that included South Korea, Japan, China, Russia and the United States. North Korea secretly continued its nuclear program, but the banking sanctions were never renewed.